This invention relates to roller belt drive motors and more particularly relates to an integrated roller belt drive motor for use in a treadmill.
Exercise treadmills are amongst the most popular physical fitness apparatus found in homes and commercial gyms. Many treadmills have walkbelts powered by DC or AC motors. Whether DC or AC motors are employed to drive the walkbelts, most include drive belt drive systems that utilize pulleys and belts to couple the motor to an elongated drive roller wheel that cooperates with an underside of the walkbelt to drive the same. The walkbelt normally includes a second elongated roller that also cooperates with the walkbelt underside and simply provides an idling function to return the belt to the drive roller.
With increased popularity of treadmills in the home has come heightened awareness that the bulky nature of the treadmill does not make it an attractive addition to the living room or bedroom for that matter. Treadmills commonly include bulky housing structures at the drive roller end to accommodate the drive motor, pulley wheel and belt systems, as well as, a flywheel which form a part of the treadmill drive system. This bulky housing problem has been addressed in the Rorabaugh U.S. Pat. No. 4,664,646 where Rorabaugh teaches the idea of utilizing an elongated electric motor and a flywheel axially associated with the motor to establish an overall silhouette that fits within a flat frame arrangement. The frame is hinged at one end and secured to a support surface in a manner that allows the frame arrangement which carries the treadmill walkbelt to be lifted and stored vertically. The use of a flywheel in a treadmill walkbelt drive system as shown by Rorabaugh is desirable because the flywheel adds rotational inertia to the drive system. The rotational inertia resists momentary increases in drag, such as when a person first steps upon the treadmill. The inertia, in practical terms, reduces the demand for torque production during such momentary resistive surges upon the motor.
The subject invention uniquely distinguishes over the Rorabaugh patent and other known prior art treadmills and treadmill motor drives in that the need for a separate drive motor and flywheel are completely removed by the inclusion of a drive motor integrated into a walkbelt drive roller. The subject invention also provides the unparalleled advantage of allowing for the inclusion of a flywheel within the belt drive roller of a treadmill.
The invention is directed to a direct drive roller motor for use in a belt drive system that engages both the direct drive roller motor and another roller, both of which rollers are mounted for rotation on a support structure. In the broadest sense the roller motor is a brushless DC motor that has an external rotor that functions as a direct drive roller. The motor has stator coils mounted on a stationary stator shaft that is physically and thermally coupled at both ends thereof to the support structure which provides in addition to support, a heat dissipating function. The stator shaft is comprised of an aluminum alloy or similar high thermal conductivity material to thereby conduct away from the stator coils via the stator shaft to the heat dissipating motor support structure, thermal energy generated by the i2R loss of the motor coils and magnetic core loss of stator electrical steel. The external rotor is comprised of a cylindrical housing which rotates about the stator shaft. The length of the cylindrical housing is substantially longer than the stator coils in order for the cylindrical housing to function as a direct drive roller for the belt drive system. The cylindrical housing has secured internally thereto, at one end thereof an annular permanent magnetic structure that cooperates with the rotating magnetic field in the stator to generate a drive torque in the cylindrical housing of the external rotor. The thickness of the cylindrical rotor housing is sufficient to not reduce the motor torque output. The rotational inertial of the rotor reduces transient loading to the belt being driven thereby. The stator shaft has secured thereto an array of magnetic field sensors mounted in a plane perpendicular to the stator shaft and the axis of rotation of the external rotor. A multi-pole magnetic ring is secured to an inner surface of the cylindrical rotor housing adjacent the array of magnetic field sensors such that rotational movement of the multi-pole magnetic ring past the array of sensors sequential produces an approximate sine wave voltage signal that is delivered to a controllable DC power source to cause a sine wave current to be generated and delivered to the stator coils to produce the rotating magnetic field in the stator.
It is therefore a primary object of the invention to provide a direct drive roller motor that is integrated into a belt drive roller thereby eliminating the need for a separate motor and pulley system to drive the belt drive roller.
Another principal object of the invention is to provide a DC brushless direct drive roller motor that has its efficiency enhanced by means of a thermally conductive stator support shaft that dissipates thermal energy generated by i2R loss of the motor coils and magnetic core loss of stator electrical steel by means of the heat dissipating nature of the motor support structure to which the stator is secured.
Yet another object of the invention is the cylindrical walled external rotor structure that functions as a flywheel to enhance torque delivered to a belt driven thereby when the belt experiences transient loading.
Still yet another object of the invention is the provision of a treadmill with a motor integrated into a drive roller which reduces total treadmill length and/or width, while simultaneously creating an overall treadmill silhouette that enhances ease of storage.
These and other objects, advantages and features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.